This invention relates to a brake control valve assembly, particularly useful in vehicle braking systems and, more particularly, to such an assembly which assures an increased effectiveness of rear wheel braking upon failure of the hydraulic system associated with front wheel brakes.
According to the conventional dual-system tandem master cylinder mechanism generally used in automobile brake systems, when the front hydraulic system fails, merely the braking pressure of the same magnitude as provided by brake fluid pressure in the rear master cylinder during the normal operation is transmitted to the rear wheel cylinders. Even in case a proportioning valve with a by-pass circuit is incorporated, such proportioning valve is disabled and the braking pressure equal to brake fluid pressure in the rear master cylinder is transmitted by way of a by-pass valve. Consequently, when trouble should occur in the front hydraulic system, no satisfactory braking force would be provided by brake fluid pressure from the rear master cylinder of the type designed such that maximum brake fluid pressure stays lower than the limit point of rear wheel locking force in the front and rear wheel braking force curve.